This invention generally relates to tire and wheel constructions for road vehicles and a particular object thereof is to provide an improved wheel which is fitted with a tubeless or tubed tire having a lower rolling friction coefficient and thus a lower resistance to forward movement of a car equipped with the invention.
Problems pertaining to the decrease of rolling resistance in tires and wheels, which is essentially caused by the work dissipated due to the deformation of the carcass and in general of the pneumatic structure of the wheel, have long been thoroughly considered by this applicant. The study has involved singling-out and analyzing the conditions by which such resistance is caused.
In particular, considerations pertinent to phenomena and to conditions associated with the deflection of a loaded tire on the ground and to deformations brought about therein, can be found in U.S. Pat. No. 3,830,272 granted to the applicant on Aug. 20, 1974. Further proposals by this applicant concerning the problems can be found in U.S. patent application Ser. No. 749,664 filed on Dec. 13, 1976 now abandoned, wherein a particularly advantageous geometry of a tire cross-section in the radial plane (i.e. in the planes wherein the wheel axis is contained) is disclosed and commented on.
The phenomena occurring in tire deflection are very complex and therefore will be summarized hereinafter as far as it is needed for a better understanding of the invention. An important parameter is the change of the tire side wall curvature under load. In particular, the carrying capacity of the tire can be rationally expressed in terms of the difference r-r", wherein r is the maximum radius of multi-center curvature by which the non-deflected unloaded tire side wall is defined, while r" is the maximum radius of multi-center curvature by which the portion of the side wall which is free to deflect under load, is actually deflected.
It is moreover apparent that a good rolling friction coefficient of a tire and wheel is, generally speaking, in inverse ratio to the parasitic resistances standing in the way of the rolling. These resistances increase proportionally with the tire deflection which, as is well known, is measured in terms of the tire radius change with equality of load and inflation pressure, hereinafter simply called "deflection".
The tires of this invention are those of the so called "radial" class, i.e. comprising a structure formed by a plurality of flexible but inextensible elements (the so called "cords") which extend between the tire bead reinforcing steel wires and exactly or even approximately lie in as many radial planes. Moreover, the tires of this invention are also of the "belted" class, i.e. a practically inextensible belt is fitted in their carcass on either side of equatorial or symmetrical planes of the tire and wheel (i.e. the major plane perpendicular to the wheel axis). As is well known, such belt acts as a "containing means" for the tire perimetrical portion, standing against the tires inside pneumatic pressure. Such an annular perimetrical portion which in the conventional tire practically underlies the tread, and has a width usually smaller than that of the tread, will be called hereinafter for disclosure convenience the "contained zone". The term "tire side wall" will identify, in conformity with the wording utilized in the art, the tire side portions defined between the beads and the contained zone, such side wall being in the conventional technique the most flexurally deformable part of the whole tire, i.e. those wherein a large decrease in the local bending radius occurs when the tire is deflected against the ground under a load action.